1. Field of the Invention
The present invention relates to a transfer pressure roll used when a protective layer for coating an image (particularly an ink jet image) formed on a recording medium by a recording system such as an ink jet recording system is provided, and a transfer device and an image recording apparatus which include the transfer pressure roll.
2. Related Art
The ink jet recording system is a printing system in which liquid droplets are ejected from minute nozzles of a recording head and attached onto a recording medium such as paper thereby to form an image. Recently, as a recording medium for ink jet recording, an ink jet recording coated paper has been developed, which is formed by providing, on a base material such as paper or a film, an ink-absorption layer including porous fine particles such as silica or aluminum as a main component. In result, an ink jet image of a high quality which is equal to a silver-halide photograph has been obtained. The surface of the ink-absorption layer, which is a recorded surfaced, is worked into a surface having surface quality suitable for use of the coated paper, for example, a specular surface, a luster surface, a matt surface, and a silky surface. Particularly, the luster surface of them is a finely rough surface having fine unevenness on its surface, so that it has a unique sense of semi-glossiness. The ink jet recording coated paper worked into the luster surface is suitable for output of a photo-like ink jet image that is like a silver halide photograph.
Though use of the above ink jet recording coated paper makes it possible to obtain an inkjet image sufficient for image quality, the ink jet image is inferior to the silver halide photograph in preservability such as light resistance, gas resistance, and wear resistance under the present conditions. The preservability of the ink jet image becomes more important as the ink jet recording technology is applied more widely to digital photograph service and commercial print. It is an important problem of the ink jet recording technology to supply the ink jet image that can be preserved for a long period.
As technology for heightening the preservability and glossy level of the ink jet image, an overcoat method has been known, in which a transparent film is stuck onto a surface of a recording material on which the ink jet image has been formed (ink jet image surface) thereby to form a protective layer which coats the ink jet image. As this overcoat method, there are a cold laminating method in which while a rear sheet (separator) of a film adhering at the normal temperature is peeled off, the film is being stuck onto the image surface; a heat (hot) laminating method in which while a thermoplastic resin film having no rear sheet is heated, it is being stuck onto the image surface; and a thermal transfer method in which an image protection film formed by providing a transparent film (transferable protection layer) on a supporting body is used, and the transparent film is thermal-transferred onto the image surface. Particularly, the thermal transfer method, compared with the other overcoat methods, makes formation of a thin protective layer possible. Therefore, the thermal transfer method has an advantage that excessively glossy level is not provided on the image surface, and its method is noticeable as an overcoat method which can heighten the preservability and the glossy level without losing the natural sense and quality level of the recording matter. Related arts on the thermal transfer method will be described for example, JP-A-60-23096 JP-A-60-189486, and JP-A-61-230973.
The thermal transfer method is executed by a transfer device. Usually, as shown in FIG. 7, a recording matter and an image protection film are superimposed on each other so that an ink jet image surface is opposed to the surface of a transferable protection layer, thereby to form a laminated sheet. This laminated sheet is permitted to pass through a nip portion formed between a heat roll and a pressure roll of the transfer device which are brought into pressure-contact with each other, whereby the laminated sheet is heated by the heat roll from the image protection film side, the transferable protection layer is melted and attached on the ink jet image surface by use of pressure, and thereafter the supporting body is peeled off from the laminated sheet. Hereby, a recording matter with a protective layer that fits the purpose is obtained.
In the above thermal transfer method, it is important to obtain sufficiently close attachment between the ink jet image surface and the transferable protection layer. This reason is that: in case that air bubbles mix between the image surface and the protective layer due to the bad close attachment, not only the recording matter is bad to look at but also color development of the image lowers and dignity of the recording matter remarkably lowers.
However, in case that the recording matter that is to form the protective layer uses the ink jet recording coated sheet having a luster-finished surface, that is, in case that the ink jet image surface is the luster-finished surface (finely rough surface), when the thermal transfer method is executed using the conventional transfer device as usual, the transferable protection layer does not sufficiently melt-enter the concave portions of the ink jet image surface, air bubbles mix in the concave portions, and the transferable protection layer is not attached closely onto the ink jet image surface (finely rough surface) by using press. Further, by the nip pressure between the heat roll and the pressure roll, the convex portions of the finely rough surface crash and become flat. In result, the protective layer surface of the recording matter with the protective layer becomes a flat specular surface with high glossiness level, so that a unique sense of the semi-glossy level the recording matter naturally has before forming of the protective layer is damaged.